This invention relates to an electronic signal processing system together with a video scanner and receiver for producing a line drawing from a tonal image having various tones, colors, or shades.
Frequently, there is a need to reproduce manuals having line drawing illustrations wherein the line drawings are representative of photographs or other pictures having various shades or tones. For example, it is a common practice to photograph prototypal setups or laboratory arrangements to provide a pictorial illustration of the same in technical manuals, patent applications, or the like. For the purpose of conveniently reproducing such illustrations, a line drawing is desired. This invention is concerned with a system for facilitating an artist in converting such photographs into line drawings and eliminating the extent of his manual labor required during the conversion process.
In the prior art, many systems have been developed to convert images to line drawings for various other purposes, such as to improve video communications or object detection. These systems usually include an electro-optical device for scanning an image or photograph in a manner similar to the method used in standard television cameras, signal processing means to process the video signal from the electro-optical scanning device, and a video receiver and display monitor for receiving the processed signal and displaying a facsimile of the scanned image or photograph. The signal processing means employed by these systems may utilize principles of density slicing, delayed cancellation, or differentiation of a video signal to produce a pulse signal therefrom wherein said pulses represent changes in level of the video signal as the image is scanned thereby providing means to detect significant lines in the tonal image. This invention is associated with the last mentioned technique, which provides a fast, cheap and convenient means of converting tonal images to line drawings.